Hydrodesulfurization process with precoditioned catalyst



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United States Patent Ufifice 2,761,817 Patented Sept. 4, 1956HYDRODESULFURIZATION PROCESS WITH PRECONDITIONED CATALYST Sumner B.Sweetser, Cranford, and Stanley 0. Bronson H, Mountainside, N. J.,assignors to Esso Research and Engineering Company, a corporation ofDelaware N Drawing. Application June 21, 1954, Serial N0. 438,362

8 Claims. (Cl. 19628) The present invention concerns an improved processfor the desulfnrization of petroleum fractions that contain relativelylarge amounts of sulfur. It particularly relates to a desulfurizationprocess in which a petroleum fraction containing in excess of about 1.5wt. per cent sulfur is hydrodesulfun'zed in the presence of a cobaltmolybdate-type catalyst. It especially concerns a method of presulfidinga cobalt molybdate catalyst in situ so that the catalyst is markedlymore active in its ability to desulfnzize a high-sulfur content feedstock. The catalyst of particular interest to the present invention iscobalt molybdate impregnated on alumina.

It is well known in the petroleum industry to reduce the sulfur contentof a petroleum fraction by subjecting the fraction to ahydrodesulfurization operation. In this process, a sulfur-containingpetroleum fraction is contacted with a catalyst such as cobalt molybdateon alumina at a temperature of about 650 to 800 F. and a pressure ofabout 100 to 1000 p. s. i. g. The petroleum fraction is fed to thehydrodesulfurization zone at a rate of about 0.25 to 3.0 volumes of feedper hour per volume of catalyst. Hydrogen-containing gas is also passedthrough the zone at rates of between 500 and 5000 s. c. f./-bbl. offeed. Under these conditions some hydrogen is generally consumed by theprocess. Hydrogen consumption rates are usually in a range of 75 to 700s. c. f./bbl. of feed and may be even as high as 1000 s. c. f./bbl. offeed. The hydrogen consumed in the process is considered to react withunsaturated compounds in the feed to form more saturated compounds andwith sulfur to form hydrogen sulfide.

The hydrodesulfurization process may be employed on petroleum fractionsthat exist within the desulfurization zone in the liquid and/ or vaporphase. Thus, petroleum fractions including naphtha, fuel oil, kerosene,gas oil, diesel fuel, jet fuel and the like may be subjected to ahydrodesulfurization operation. Similarly, feed stocks derived fromcracking operations may be employed as well as straight-run fractionsthat are derived directly from a crude oil.

The hydrodesulfurizati-on process causes sulfur compounds within apetroleum fraction to react with hydrogen to form hydrogen sulfide. Thehydrogen sulfide and other gaseous components are separated from. theproduct stream and handled as desired. In many instances, the gaseouscomponents are scrubbed with an ethanolamine solution which serves toremove any hydrogen sulfide therefrom.

As the hydrodesulfurization process proceeds, the catalyst may graduallydeactivate and in such a case, it will have to be periodicallyregenerated by burning oi the carbon deposited on the catalyst. This isdone by passing an oxygen-containing gas through the catalyst at atemperature of between 800 to 1100 F. and a pressure of between 0 to 400p. s. i. g. The regenerating gas may contain about 1 to 21 volume percent oxygen obtained fromlair and is generally diluted with eitherrecycled flue gas or steam. The main problem in such a regeneration isthe economic removal of the heat of burning. A longer interval betweennecessary regeneration permits a slower burning rate and consequentlyless expensive provisions for heat removal. It thus follows that anygainin catalyst initial activity which permits a longer operationbetween necessary regenerations, will be particularly desirable.

To date, it has not been the practice to presulfide a cobalt rnolybdatecatalyst before employing the catalyst to desulfurize a petroleumfeedstock. This has been particularly true in those instances where thefeedstock contains more than about 0.15 wt. per cent sulfur. When thefeedstock contains less than this amount of sulfur, it has been anoccasional practice to presulfide the catalyst by first contacting itwith a petroleum fraction containing more sulfur than the feedstockitself. Specifically, petroleum fractions containing from about 0.25 to0.50 wt. per cent sulfur and especially about 0.50% have been used forthis purpose.

The presulfiding or activating step has been generally carried out attemperatures of about 550700 F., pressures of about 100 to 1000 p. s. i.g. and feed rates of about 0.5-2 volumes of feed per hour per volume ofcatalyst. The duration of the presulfiding step has been governed by thefact that a catalyst of the cobalt molybdate type is generally mostactive when it is partially sulfided. When sulfiding under theconditions described above, it has been usually desirable to employsulfiding times between about 12 and 48 hours duration.

Up to the present time, presulfiding of a cobalt molybdate catalyst hasnot been employed when the catalyst is to be used in thehydrodesulfurization of petroleum feedstocks that contain in excess ofabout 0.15% sulfur. Instead, such a feedstock is contacted directly withthe cata lyst under conventional hydrodesulfurization conditions. Thisprocedure has been especially true for feedstocks that possess in excessof 1.5% to 2% sulfur.

As mentioned earlier, the present invention is concerned with thehydrodesulfurization of high-sulfur content petroleum fractions thatcontain in excess of about 1.5% by weight sulfur. It is particularlyconcerned with petroleum fractions which contain about 2 to 6 Wt. percent sulfur; and it is a particular object of the invention to rendercobalt-molybdate type catalysts more active for the desulfurization ofsuch feed stocks. It is a further object of the present invention toprovide a means for increasing the activity of cobalt-molybdateonalumina for desulfurizing .a high sulfur content petroleum fraction in ahydrodesulfurizatiou operation which utilizes an activated cobaltmolybdate-type catalyst. As described earlier, particularly elfectivecatalysts for this purpose are formed by the impregnation of aluminawith cobalt mclybdate. Such catalysts are Well known in the art and areconventionally prepared, for example, by impregnating alumina with anammoniacal solution of cobalt and molybdenum salts. The catalyst isdried and decomposed to convert the cobalt and molybdenum salts to theoxides.

Before employing a catalyst of the type described above in thehydrodesulfurization of a high-sulfur feedstock, the

catalystin accordance with the present inventionis first contacted andpresulfided with a petroleum fraction which contains about 0.2 to 1.0wt. per cent sulfur and preferably about 0.5 wt. per cent sulfur. Thehydrocarbon fraction may boil in a range of about 300 to 700 F., and itis preferred that the fraction boil from about 330 to 550 F. Thefraction may contain straight-run hydrocarbons as well as hydrocarbonsthat are derived from cracking operations. It is preferred, however,that the petroleum fractions be characterized by possessing from aboutto 110 mgs. of mercaptan sulfur per 1111. Straight run fractions thatcontain about 99 mgs. of mercaptan sulfur per 100 ml. have been found tobe especially effective.

In accordance with the present invention, a cobalt molybdate on aluminacatalyst is presulfided by contacting it with a hydrocarbon fraction ofthe type described immediately above. It is preferred that thehydrocarbon fraction be passed through the catalyst at a feed ratebetween about 0.5 and 2.0 volumes of feed per hour per volume'ofcatalyst. A particularly preferred feed rate is about 1.0 v./h./v. Anoperating temperature of about 550 to 650 F. and an operating pressureof about 100 to 250 p. s. i. g. may be employed. It is particularlypreferred that an operating temperature of about 600 F. and a pressureof about 200 p. i. g. be employed. The hydrocarbon fraction may be inthe liquid andor vapor phase during the presulfiding step; and it may bepassed upflow or downflow through the bed. Particularly effectiveresults have been obtained with about 80% of the fraction in the vaporphase within the reaction zone and with downflow operation.

When the presulfiding operation is'initiated, it has been observed bychemical analyses that the product stream generally shows very littledesulfurization. After a short period of time, however, the catalystbegins to combine with the sulfur in the presulfiding feed; and analysesof the product stream reveal a gradually increasing degree ofdesulfurization taking place. After about 12 to 36 hours of thepresulfiding operation, it has been found that the degree ofdesulfurization of the presulfiding feed reaches an equilibrium value.In other words, the sulfur content of the product stream settles out ata substantially constant value. At this point the catalyst, which maycontain from 15% to 65% by weight of the sulfur that would be requiredif all of the cobalt molybdate were converted to the thiomolybdate, isactivated; and the desulfurization operation is commenced.

During the presulfiding operation it is desired that a hydrogen rate tothe reaction zone of about 500 to 3000 s. c. f./bbl. of feed beutilized. It is particularly preferred that a hydrogen rate of about1000 s. c. f./bbl. be used.

Following the presulfiding step, a feed stock to be desulfurized ispassed through the bed of presulfided catalyst. As mentioned earlier, acatalyst which'has' been presulfided according to the present invention,is particularly effective for use in the hydrodesulfurization ofpetroleum fractions that contain in excess of about 1.5 wt. per centsulfur and especially about 2 to. 4.5 wt. per cent sulfur. Such a feedstock is passed through the presulfided catalyst at a rate of about0.253.0 volumes of feed/hour/volume of catalyst (v./hr./v.) at atemperature of about 650800 F. and a pressure of about 1!00l000 p. s. i.g. A hydrogen feed rate of about 500-5000 s. c. f./bbl. of feed should.be employed.

Regeneration of the catalyst may be required periodically, dependinglargely upon the nature of the feed stock. Some feed stocks such asstraight-run distillate petroleum fractions cause very little or nodegradation of the catalyst; and the catalyst may be employed in such,cases for months without regeneration. Indeed, frequently norcgeneration is required. Feed stocks derived from cracking or cokingoperations, on the other hand, degrade a catalyst much more rapidly, andmore frequent regenerationsvare therefore necessary. Even in theseinstances, however, the catalyst need almost never be regenerated morethan once a week. But whenever a catalyst is regenerated, it isgenerally desirable to reactivate the catalyst by the presentpresulfiding procedure before it is returned to hydrodesulfurizationservice. A

The present invention may be better understood by reference to thefollowing examples which illustrate specific examples of theinvention'and preferred modes of carrying out the same.

Example I A conventional cobalt molybdate on alumina catalyst in theform of A x 4 cylindrical pills was charged to a reaction zone. Here thepills were presulfided by contact with a West Texas light straight-runheating oil.

The heating oil had a boiling range of about 330530 F., an A. P. I.gravity of about 39, a sulfur content of about 0.5 wt. per cent andcontained about 99 mgs. of

mercaptan sulfur per 100 ml. The heating oil was passed through thecatalyst in a downflow operation at 600 F., 200 p.- s. i. g. and 1v./hr./v. for a period of 24 hours.

The 24 hour time had been selected on the basis of preoil, the catalystwas then contacted in a downfiow manner with a coker gas oil possessinga boiling range of 430- 1050 R, an API gravity of about 15, and a sulfurcontent of about 4 wt. per cent. The coker gas oil was derived byconventional fluid coking at 1000 F. of a 1050 F.+ residuum from a WestTexas crude. The

residuum comprised about of the total crude;

It will be noted that the feed rate of the various liquid fractions tothe catalyst zone is expressed in this example and throughout thepresent description in terms of volumes of liquid/hour/volume ofcatalyst. A hydrogenfeed rate of about 3500 s. c. f./bbl. of coker gasoil was employed during the hydrodesulfurization reaction. The reactionadditionally was carried out at a temperature of 750 F., a pressure of400 p. s. i. g. and feed rate of 0.5 v./h r./v. As a result of thistreatment, the sulfur content of the coker gas oil was reduced from theinitial value of 4 wt. per cent to a value of about 0.40 wt. per cent.

. required.

realized in Example 1.

Example 11 those presented in Example I. In this instance, however,

the catalyst was not first activated by treatment with'the straight-runheating oil. Instead, it was initially and directly contacted with thecoker gas oil. In the absence of the pretreatment with the virginheating oil, the coker gas oil experienced a sulfur reduction to a valueof only 0.49 wt. per cent instead of the 0.40 wt. per cent value It isapparent from these data that the presulfiding step employing the Virginheating oil is .very effective in increasing the activity of thecatalyst.

Example III In this example, samples of a West Texas heavy straight-rungas oil of 24.4 API gravity and a 500 to 1050 F, boiling range werehydrosulfurized over a cobalt molybdate on alumina catalyst (of the typein Examples I and II) with and without pretreatment with a West Texaslight straight-run heating oil. Thus, in a first procedure a sample ofthe heavy gas oil was passed directly and downflow through a bed of thecatalyst at 700 F., 400 p. s. i. g., 1.0 v./hr./v. and at a hydrogenrate of 1500 s. 'c. f./bbl. of feed. Under these conditions the heavygas .oil experienced a sulfur reduction from 2.1 wt. per cent sulfur to0.16 wt. per cent sulfur. The gas oil further experienced an increase ingravity up to a value of 28.7 API.

In a second treating procedure, the catalyst was first contacted for 24hours with a West Texas light straightrun heating oil (39 API, 330540 F.boiling range and 0.5 wt. per cent sulfur and 99 mgs. of mercaptansulfur perl00 ml.) at 600 F., 200 p. s. i. g., 1 v./hr./v. and 1000 s.c. f./bbl. hydrogen rate. Following this pretreatment procedure, thecatalyst was then contacted with The run was terminated beforeregeneration was another portion of the West Texas heavy straight-rungas oil under the same hydrodesulfurization conditions described earlierin this example. In this instance, however, the heavy gas oil realized asulfur reduction to 0.11 wt. per cent sulfur, thereby demonstrating themarked eflectiveness of the presulfiding procedure in increasing theactivity of the catalyst.

The foregoing examples are intended to illustrate specific applicationsof the present invention. It will be understood that the presentinvention is not to be limited, however, in its scope to theseparticular examples. Thus, it will be noted that the presulfiding andhydrodesulfurizing reactions of the present invention may be employedusing fixed beds, moving beds or fluidized beds of catalyst. Suchmodifications of the invention are considered to be well within theability of persons skilled in the art to realize.

It will further be appreciated that the catalyst may be employed instructural forms other than the x 75 cylindrical pills presented in theexamples. Furthermore,

the catalyst may contain a small amount of silica to stabilize it in amanner known to those skilled in the art.

It will further be realized that the present invention may be used incombination with other petroleum refining processes such as catalyticprocesses including hydroforming, platforming, cracking, and the like.It is particularly contemplated that gas oil fi'actions derived from thepresent desulfurization process be employed as feed stocks to catalyticcracking operations.

Piping, pumps, valves, instruments, heat exchangers,

furnaces and other equipment conventionally employed to operatehydrodesulfurization processes may be utilized without departing fromthe spirit or scope of the present invention. Similarly, the hydrogenutilized in the present process may be derived from any of theproduction sources that are contemplated for use in connection withhydrodesulfurization processes.

What is claimed is:

1. In the catalytic hydrodesulfurization of a petroleum feedstockcontaining from 2-6 wt. per cent sulfur with the aid of a cobaltmolybdate-type catalyst, the improvement of which comprises contactingthe catalyst at about 300-700" F. and 100-250 p. s. i. g. for about12-36 hours with about 0.5 to 2.0 v./hr./v. of a petroleum fractionwhich boils within the range of about 330-550 F. and which containsabout 0.5 wt. per cent sulfur, said fraction further being characterizedby containing about 90-110 mgs. of mercaptan sulfur per 100 ml. of saidfraction, said preactivating being carried out in the presence of about1000 s. c. f. of Hz/bbl. of fraction and thereafter treating a petroleumfeed stock containing from 2 to 6 wt. per cent sulfur in contact withsaid reactivated catalyst under hydrodesulfurizing conditions attemperatures above about 650 F.

2. In the hydrodesulfurization of petroleum feedstocks which containabout 24.5 wt. per cent sulfur by means of a cobalt molybdate-typehydrodesulfurization catalyst,

the improvement which comprises contacting the catalyst with a petroleumfraction that boils within the range of about 330-550 F., said fractioncontaining about 0.5 wt. per cent sulfur and about 99 mgs. of mercaptansulfur per 100 ml., said fraction being contacted with said catalyst atabout 600 F. and 200 p. s. i. g. at 1.0 v./hr./v. in the presence ofabout 1000 s. c. f. of hydrogen per barrel of petroleum fraction forabout 12-36 hours and thereafter treating a petroleum feed stockcontaining from 2 to 6 wt. per cent sulfur in contact with saidreactivated catalyst under hydrodesulfurizing conditions at temperaturesabove about 650 F.

3. Process as defined in claim 2 in which the fraction used forpreactivating the catalyst consists of straight-run hydrocarbons and thefeed stock consists of cracked hydrocarbons.

4. Process as defined in claim 1 in which the sulfided catalyst containsfrom 15 to wt. per cent of the sulfur theoretically required to changethe cobalt molybdate to cobalt thiomolybdate.

5. Process as defined in claim 2 in which the presulfiding is carriedout for a period of about 24 hours.

6. The method of catalytically hydrodesulfurizing a high-sulfur contentpetroleum feedstock with a cobalt molybdate-type catalyst whichcomprises in combination presulfiding the catalyst in a reaction zone atabout 550-650 R, 100-250 p. s. i. g. and 0.5-2.0 v./hr./v. with a firstpetroleum fraction which boils Within the range of about 300-700 F. andwhich contains about 0.2 to 1.0 wt. per cent sulfur, said fraction beingfurther characterized by containing about -100 mgs; of mercaptan sulfurper ml. of fraction, said catalyst being sulfided in the presence ofabout 500 to 3000 s. c. f. of Hz/bbl. of fraction until the degree ofdesulfurization of the fraction reaches an equilibrium value, thereafterpassing a second petroleum fraction comprising the highsulfur feedstockcontaining in excess of 1.5 wt. per cent sulfur through the presulfidedcatalyst at a rate of about 0.25 to 3.0 v./hr./v., a temperature of650-800 F. and a pressure of 100-1000 p. s. i .g. in the presence offrom 500-5000 s. c. f. of Ha/bbl. of feedstock.

7. A process as defined in claim 6 in which the said first petroleumfraction contains about 0.5 wt. per cent sulfur and the feedstockcontains about 2 to 4.5 wt. per cent sulfur.

8. A process as defined in claim 7 in which the said first petroleumfraction contains about 99 mgs. of mercaptan sulfur per 100 m1. of saidfraction.

References Cited in the file of this patent UNITED STATES PATENTS2,143,078 Lyman et al. Jan. 10, 1939 2,337,358 Szayna Dec. 21, 19432,604,438 Bannerot July 22, 1952 2,647,857 Home Aug. 4, 1953 2,656,302Porter et al. Oct. 20, 1953

1. IN THE CATALYTIC HYDRODESULFURIZATION OF A PETROLEUM FEEDSTOCKCONTAINING FROM 2-6 WT. PER CENT SULFUR WITH THE AID OF A COBLATMOLYBDATE-TYPE CATALYST, THE IMPROVEMENT OF WHICH COMPRISES CONTACTINGTHE CATALYST AT ABOUT 300-700* F. AND 100-250 P. S. I. G. FOR ABOUT12-36 HOURS WITH ABOUT 0.5 TO 2.0 V./HR./V. OF A PETROLEUM FRACTIONWHICH BOILS WITHIN THE RANGE OF ABOUT 330 550* F. AND WHICH CONTAINSABOUT 0.5 WT, PER CENT SULFUR, SAID FRACTION FURTHER BEING CHARACTERIZEDBY CONTAINING ABOUT 90-110 MGS, OF MERCAPTAN SULFUR PER 100 OF SAIDFRACTION, SAID PERACTIVATING BEING CARRIED OUT TO THE PRES ENCE OF ABOUT1000 S. C. F. OF H2/BBL OF FRACTION AND THEREAFTER TREATING A PETROLEUMFEED STOCK CONTAINING FROM 2 TO 6 ET. PER CENT SULFUR IN CONTACT WITHSAID REACTIVATED CATALYST UNDER HYDRODESULFURIZING CONDITIONS ATTEMPERATURES ABOVE ABOUT 650* F.